The present invention relates to heart assist devices and more particularly to a novel, highly effective heart assist device of an umbrella-like design, and which is small and mechanically fool-proof.
Heart assist devices are presently employed to assist the pumping function of the heart either for use in patients having weakened heart conditions and/or during certain surgical procedures or treatments. Devices of this category generally in use at present comprise intra-aortic balloons, Anstadt Cups and partial bypass systems. Partial bypass systems typically comprise apparatus external to the body and coupled thereto by tubular means for assisting in the blood pumping function of the heart.
Intra-aortic balloon assist devices are comprised of a pneumatic pump system to operate an intraaortic balloon positioned in the aorta in close proximity to the aortic arch adjacent to the left ventricle. The balloon is periodically and regularly inflated and deflated in synchronism with the beating heart and is typically operated under control of the R-wave of the patient's heart. For example, the balloon is suddenly collapsed just as the left ventricle of the heart starts to eject the blood within it. This abrupt reduction of volume in the aorta, due to the collapse of the balloon, reduces the pressure therein and thereby permits the ventricle to eject the blood more readily and completely. Immediately after ejection, the balloon is then inflated, causing an increase in volume and pressure within the aorta during diastole, or the relaxation phase of the heart muscle, when the muscle is in turn perfused or supplied by oxygen in the blood at a level somewhat proportional to this diastolic pressure. Thereby, this higher pressure causes improved blood circulation, especially to the heart and also to the brain.
The work reduction of the left ventricle due to the balloon's deflation is conventionally represented by the product of the pressure reduction times the volume of blood of the ejection. This is the equivalent "potential energy" equation from physics relating to equivalent height (pressure) times weight (volume).
It is believed by the present inventor that the other energy component, namely kinetic energy, is even more relevant to improving the work reduction of the left ventricle, especially when more extensive assistance is to be provided to a failing heart with a balloon limited in volume by the small arteries of the patient. This kinetic energy is equivalent to 1/2.times.m.times.v.sup.2. In other words, it is proportional to the weight of the blood displaced by the balloon times the square of the velocity of the blood as it moves away from the ventricle towards the deflating balloon.
In contrast to the foregoing, retrograde blood flow coming from the aorta below the balloon and the lower extremities during and due to the deflation of the balloon will move upward and oppose the downward flow from the heart. It therefore opposes the kinetic energy work reduction to the left ventricle.
It is, therefore, important to provide a simple and yet highly effective mechanical assist device which is designed so that the retrograde flow resulting from balloon deflation as well as undesirable consequences of retrograde flow, may be eliminated or significantly reduced.